1. Field of the Invention
The present invention relates to a seat track structure employed in a seatbelt system for a vehicle designed to protect an occupant in an emergency situation of the vehicle, the seat track structure incorporating a belt anchor for anchoring the seatbelt system to the body of the vehicle.
2. Description of the Related Art
In general, a seat for an occupant of a vehicle is mounted on the floor of the vehicle body through a seat track constituted by a lower rail which is secured to the floor surface and an upper rail which is secured to the seat and adapted to be slidable on the lower rail together with the seat.
On the other hand, the inner belt of the seatbelt system is secured directly to the floor of the vehicle body without any relation to the seat track. Therefore, the tension generated in the webbing by the inertia acting on the occupant's body when an emergency situation of the vehicle occurs is directly supported by the floor.
There is another conventional arrangement in which the inner belt is secured to the seat so that the webbing can be fastened to the body of the occupant at a constant position at all times regardless of the occupant's adjusting the position of the seat in the longitudinal direction of the vehicle. With this arrangement, however, when an emergency situation of the vehicle occurs, the seat track is subjected to a large load which acts such as to separate the upper and lower rails from each other, and it is therefore necessary to make the seat track more solid.
The lower rail of the seat track is generally bent at the upper end thereof in the horizontal direction, and the upper rail is mounted on the lower rail in such a manner as to cover this bent portion of the lower rail. Therefore, in order to strengthen the seat track, it is necessary to enlarge the width of the seat track, and this leads to a reduction in the leg space for the occupant in the rear seat.
To overcome this problem, a structure has already been proposed in which, despite that the inner belt is secured to the seat, the seat track is not subjected to a large load even when an emergency situation of the vehicle occurs (see, e.g., Japanese Utilility Model Laid-Open No. 257/1985). With this conventional arrangement, however, it is necessary to lay a rail and the like on the vehicle body separately from the seat track, so that the structure is complicated.
The present inventors have already proposed a structure in which the seat track is arranged vertically, and a load which is transmitted to the seat track from the belt anchor is supported by a retaining means which is movable in the lateral direction of the vehicle and extends through the seat track, thereby preventing separation of the upper and lower rails (see U.S. patent application Ser. No. 863,423).
In this structure, however, the bracket connecting the lower rail to the vehicle body is applied only for fixing the lower rail to the vehicle body. Also, since a part of a large load acting on the belt anchor in the emergency situation acts such as to separate the bent portion of the lower rail and the end portion of the belt anchor received in the bent portion from each other, it is preferable to strengthen a resistance to the separation therebetween.